Cabbage Worm Eradication

This, my friends, is a tale of a very hungry caterpillar that goes by the name of Pieris rapae or Cabbage Worm. Unlike the Children’s classic by Eric Carl, this garden pest doesn’t dine on watermelon and cupcakes but instead your beloved vegetable garden. He also doesn’t turn into a beautiful butterfly at the end of the story but instead a silvery white moth.

What are cabbage worms exactly? Well, contrary to their name they aren’t worms. They are small green caterpillars with big appetites. They love plants in the cabbage family, including cabbage, broccoli, cauliflower, kohlrabi, kale, and collard greens. Based on my experience, this pest will also attack potato, tomato, spinach, cucumber, pumpkin, watermelon, mint, and oregano leaves.

Don’t underestimate his size. I find the cabbage worm to be one of the most destructive pests in my vegetable and herb garden. This small caterpillar can cause mass destruction to your plants in a matter of just one evening.

Night before cabbage worm attack…Morning after cabbage worm attack!

I’ve been looking for a good way to control these pests. I’ve scoured blogs, gardening websites, and even talked to a few local Master Gardeners. After several growing seasons of testing out tips and tricks for cabbage worm eradication, I am happy to share with you my top 3 favorite organic methods.

How to Identify a Cabbage Worm

First things first – it’s important to identify that the cabbage worm is indeed to blame for your plant damage. The holes they leaves behind can be indicative of several other pests, including the pesky grasshopper.

This picture isn’t necessarily topic relevant, but I had so much fun taking it I thought I’d share it anyways. 🙂 Now back to the topic at hand…

The cabbage worm is velvety green in color and has many short fine hairs and faint yellow strips down its side and back. It can reach a maximum length of about 1-1/4″.

Adults are white or pale yellow butterflies with three or four black spots on their wings. They are frequently noticed fluttering about the garden from early spring to late fall.

They typically eat holes in the leaves and hide out on the bottom side of foliage. Their green color makes them difficult to detect.

What Cabbage Worm Damage Looks Like

In the larval stage, cabbage worms will feed on the surface layer of leaves, leaving behind translucent, tissue-like scars.

As they grow, they chew large, irregular holes in the leaf foliage sometimes only leaving the stem stalk behind. Dark-green pellets of excrement can be found on the leaves wherever they go.

Organic Cabbage Worm Control

Now onto the good stuff- how to kill these nasty little buggers. First, let me highlight several popular methods I tried that didn’t work.

Methods that DID NOT Work in my Garden (Don’t waste your time on these):

“Plant tomatoes, onions, garlic, sage, and rosemary near your cabbage, kale, broccoli, cauliflower, and lettuce.” Several blogs suggested this as a way to repel the cabbage worm. Not only did this not work, I found the pests feeding on some of my tomato, garlic, and sage leaves.

“Hand pick them off.” When the caterpillars initially hatch, they are so small that you practically need a magnify glass to see them. They can still cause mass damage at this stage and quickly multiply. Picking them off as your method of eradication may slow them down, but is a waste of time in my opinion.

“Spray a mixture of chili powder and garlic on your plants.” Several gardening websites suggested this as a method to repel the cabbage moth. I tried different ratios of garlic to chili powder having no luck of effective repellent. This method did not work and made my garden smell like an old shoe.

Let’s get to methods that proved effective in my garden to repel the cabbage moth, prevent infestation, and treat infestation.

Methods that DID WORK in my Garden (Try these!):

1. Home-made cabbage moth repellent recipe (via Todd Jones, Master Gardener and volunteer at the Garden of the Sun, Fresno): 1/2 cup dish washing liquid, 1/2 cup fish emulsion, a gallon of water, and a can of beer. Mix it up in a large pump-type sprayer and spray all susceptible plants in the garden. This recipe worked great when used early in the season as a cabbage moth repellent.

2. Floating row cover: If you don’t have a problem already, use a floating row cover to keep the moths out of your susceptible plants. If they can’t get to them, they can’t eat them.

3. Bacillus thuringiensis, Bt:(If you’re reading this, you probably already have an infestation. In that case, this method is your best course of action.) Bt is a biological insecticide (actually a bacterium that only infects caterpillars) that will control an existing cabbage worm problem. It’s inexpensive, extremely effective, and easy to use. Simply spray the leaves, all surfaces, with Bt solution. The cabbage worms will eat the leaves, become infected by the Bt, and perish 6-8 hours later.

And if all else fails the worms and moths make a great “pet” for the kids.

Not a cabbage moth in this picture, but my son Benjamin does enjoy his his “pet” bugs.